Stereoselective, Base-Induced Formation of Bicyclo[2.2.1]heptanones and Bicyclo[3.2.1]octanols From the Products of Conjugate Addition of Lithiated Allylic Sulfoxides and Phosphine Oxides to Cyclopent-2-enone

Abstract

Treatment of the neutral cyclopentanone adducts derived from the conjugate addition of each of lithiated 3-methylbut-2-enyl phenyl sulfoxide, (E)- and (Z)-but-2-enyldiphenylphosphine oxide to cyclopentenone with potassium t-butoxide results in intramolecular conjugate addition of the enolate arising from deprotonation at C5 of the cyclopentanone with the vinyl sulfoxide or phosphine oxide in the side chain togenerate bicyclo[2.2.l]heptanones in good yields. The use of an excess of lithium diisopropylamide at low temperature on the other hand results in kinetic deprotonation of the vinylic sulfoxide or phosphine oxide, and intramolecular nucleophilic addition of the resulting vinylic anions to the carbonyl groups in the respective adducts to generate bicyclo[3.2.l]octanols in acceptable yields. Application of the latter reaction to the lactone adduct of lithiated 3-methylbut-2-enyl phenyl sulfoxide and crotonolactone results in ring opening of the lactone to give a 2-(phenylsulfinyl)cyclohex-2-enone.